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The most common forms of injectable testosterone in the US include Testosterone Cypionate, Testosterone Propionate, Testosterone Enanthate, or a combination of different ester types (ester blend). An 'ester' is basically a chain composed of Hydrogen, Carbon, and Oxygen atoms which are attached to the testosterone molecule which must be broken down creating a 'timed release" in the body once injected. Even though the testosterone molecule remains the same no matter the ester, each one can yield different results by the way they are metabolised in the body once injected. For testosterone replacement therapy the ester does not matter as much as the timing and frequency of injections. The ultimate goal should be to restore total testosterone to a good range, or 'optimal' range, with about 2%-4% free testosterone. You can acheive this using any ester if the injection is timed correctly. The problem with using blended esters instead of a single ester is that blends can cause testosterone levels to become unpredictable or too erratic for replacement therapy. Blended preparations using multiple testosterone esters look great on paper, and they can be easier for a compound pharmaceutical rep to sell, but they are not as easy to work with clinically. One reason a doctor might include more than one ester, for example a combination of propionate and cypionate, is to provide a more aggrssive release pattern "spike" in those men who sometimes feel better due to the way they metabolize testosterone once injected. Since everyone responds differently you want to make sure you are following up until response is established. I have tried every combination of ester available (and not available) and still prefer testosterone cypionate by itself as it is predictable for me.
Always remember that each of these forms is simply testosterone, the hormone molecule remains unchanged, and the only difference is the attached "ester" which determines the half-life within the body. 'Cypionate', 'enanthate', and 'propionate' are all esters.
Enanthate: This is metabolized in roughly 4-5 days. It can even remain in the body (in very small amounts) for 2 weeks. 100mg of Testosterone Enanthate yields ~73mg of actual testosterone, the rest is ester weight. Injections can be administered every 5 days. As we all know everyone is unique in their response to drugs but from what I have seen in my experience the approximate starting doses which may bring a patient within optimal ranges (650ng-1100ng) is 100mg-200mg IM every 5-7 days. Of course many factors come into play including the patient's baseline levels and biology.
Cypionate: This ester has a half-life of 8 days resulting in the slow metabolism of hormone once injected. Providers commonly recommend injecting cypionate once to twice per week to maintain stable hormone levels. 100mg of Testosterone Cypionate yields~68mg of actual testosterone.
Propionate: This is a faster acting ester which can peak in the blood within hours and be fully metabolized over 3 days. Injections are commonly administered every 2-3 days. Since it metabolizes so quickly, and needs to be administered frequently, it is easy to stabilize levels and optimizes blood-testosterone-levels quickly. 100mg of Testosterone Propionate yields ~93mg of testosterone.
Other Esters found in TRT medicine may include;
Aqueous Testosterone Suspension: No-Ester. Requires frequent IM injections since it remains in the body only for a few hours. (Very painful injection). The risks outweigh the benefits when it comes to Testosterone Suspension and we do not recommend prescribing this particular ester.